Thermal analysis, is a technique for determining and predicting the microstructure in which a certain molten substance, such as a molten metal or a molten alloy, will solidify. Such a thermal analysis is basically carried out by recording a so-called cooling curve showing the temperature variations as the molten sample transitions from the liquid state to the solid state, and then comparing the curve with pre-recorded calibration data. Cooling curves have been extensively used in the experimental study and production control of cast irons.
Thermal analysis is typically carried out by taking a sample of the melt to be analysed, and bringing the sample into a sample vessel. Then, cooling curves are recorded in the sample during solidification by means of temperature-responsive means, such as thermocouples or pyrometers.
Methods for predicting the microstructure with which a certain cast iron melt will solidify are known in the art. WO 99/25888 and WO 92/06809 disclose two examples of such methods. When carrying out the methods of both WO 99/25888 and WO 92/06809, a sample of molten cast iron is taken and subsequently the sample is transferred to a sample vessel. When the sample solidifies in the vessel, two cooling curves are recoded. One of the curves is recorded in the centre of the sample, whereas the other is recorded close to the sample vessel wall. Examples of suitable sample vessels that can be used in these methods are disclosed in WO 96/23206 and WO 99/28726.
When carrying out such prediction methods, it is essential that the underlying temperature measurements are obtained under constant conditions. A substantial amount of calibration has to be carried out. The sample amounts must be substantially identical. The sample vessels in which the cooling curves are recorded must also be substantially identical. Small differences regarding the sample vessels, sample amounts, thermocouple locations, etc. can lead to prediction errors. The industrial tolerance level regarding castings having an erroneous microstructure is very low, due to the substantial costs involved in quality control and potentially recalling of sold products. It is therefore essential to be able to carry out such thermal analysis methods for predicting the microstructure in which a certain cast iron melt will solidify under as constant conditions as possible.